1. Field of the Invention:
The present invention relates to a coating composition for optical plastic moldings. The term "optical plastic moldings" as used in this specification implies plastic moldings for use as spectacle lenses, camera lenses, and other optical parts.
2. Description of the Prior Art:
Optical plastic moldings are expected to find use in various fields on account of their outstanding characteristic properties such as light weight, good processability, and high impact resistance. However, their use has been limited owing to their low hardness and poor resistance to scratch, light, and heat. They tend to decrease in hardness and resistance to scratch and light as they increase in refractive index. To eliminate these disadvantages optical plastic moldings are usually provided with hard coating film. The present inventors had previously proposed a coating composition for this purpose (Japanese Patent Publication No. 42665/1982). It is composed of a silane compound having an epoxy group, carboxylic acid, and curing agent and is applicable to dyeable optical plastic moldings. It has been put to practical use.
Unfortunately, this coating composition has been found to have a disadvantage that it brings about optical interference when it is applied to optical plastic moldings having a refractive index higher than 1.6, because it gives rise to a coating film having a refractive index in the neighborhood of 1.5. The interference is detrimental to the performance of the optical plastic moldings. Another disadvantage is that the coating film becomes poor in adhesion as the optical plastic moldings are deteriorated by light.